2,7-Bis(4-aminophenoxy) naphthalene (BAPN), a naphthalene-containing diamine, was synthesized and polymerized with a 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) to obtain a polyimide (PI) via thermal imidization. To enhance the thermal and mechanical properties of the polymer, PI-Montmorillonite (MMT) nanocomposites were prepared from a DMAc solution of poly(amic acid) and a DMAc dispersion of MMT, which were organo-modified with various amounts of n-dodecylamine (DOA) or cetylpyridium chloride (CPC). FTIR, XRD, and TEM (transmission electron microscopy) were used to verify the incorporation of the modifying agents into the clay structure and the intercalation of the organoclay into the PI matrix. Results demonstrated that the introduction of a small amount of MMT (up to 5%) led to the improvement in thermal stability and mechanical properties of PI. The decomposition temperature of 5% weight loss (T-d,T-5%) in N-2 was increased by 46 and 36 degrees C in comparison with pristine PI for the organoclay content of 5% with DOA and CPC, respectively. The nanocomposites were simultaneously strengthened and toughened. The dielectric constant, CTE, and water absorption were decreased. However, at higher organoclay contents (5-10%), these properties were reduced because the organoclay was poorly dispersed and resulted in aggregate formation. The effects of different organo-modifiers on the properties of PI-MMT nanocomposite were also studied; the results showed that DOA was comparable with CPC. (c) 2006 Wiley Periodicals, Inc.